The most important rule that Mr Trump can stick to, is to let the Queen lead - this applies to everything, from the topic of a conversation to where they're walking, to when a meal has ended. The Queen is always in charge.

Donald Trump might have been elected President of the US, but the Queen is the Queen and should be treated with deference.

Don't bow from the waist

Donald Trump could give a little head bow, like this. Credit: PA

Since neither the US President or his wife Melania are British citizens, they do not have to bow or curtsey to the Queen, but it's still a nice thing to do.

Should Mr Trump feel like giving a little bow though, this is all it should be: little.

The bow should be a neck bow, not a waist bow - which is what you do when you've finished a theatrical performance.

If the First Lady does give a curtsey, this is simply the right foot behind the left with a slight bob.

Don't offer a handshake

The Queen will offer a handshake if she wants to. Credit: PA

After (perhaps) giving a little bow on meeting the Queen, the President should not, under any circumstances, offer his hand for a handshake.

The Queen doesn't always shake hands with people, but if she wants to, she will offer her hand (that point about letting the Queen lead again), at which point the President (who has in the past seemed to need some guidance on handshake etiquette) should accept and pump up and down two or three times.

Mr Trump shouldn't grip the 92-year-old's hand too hard, nor should he clasp it with the other hand as well, or shake too vigorously.

After the handshake, the President's hands should return to his sides.

Don't call the Queen Liz

Not Liz. Credit: PA

This would probably be the ultimate mistake.

When you first meet the Queen, the correct way to address her is "Your Majesty", and then after that it's "Ma'am" (pronounced like ham).

When ending a conversation or leaving, you can revert back to "Your Majesty" for the final time.

Don't touch the Queen

Other than shaking the Queen's hand, there should be no other physical contact between Mr Trump and the Queen.

This includes touching someone on the arm when talking to them, or guiding them when walking.

There should definitely be no hand-holding à la Theresa May.

Don't lead the conversation

The Queen should lead the conversation. Credit: PA

Again that point about letting the Queen take charge and acting in a deferential manner towards her.

When talking to the Queen, Mr Trump should let her begin the conversation and also lead it.

This will ensure that the exchange does not go off track, into personal matters, or things the may not wish to discuss.

Don't talk about politics

Keep clear of politics when talking to the Queen. Credit: PA

One of the topics the Queen will not wish to discuss is politics, so Mr Trump must not talk about this with the Queen.

All members of the Royal Family are politically neutral, so engaging them in a conversation about politics would be a very big blunder.

Safer topics of conversation the 72-year-old could involve the monarch in are things such as the weather (as a Brit the Queen will probably enjoy this) or the Royal corgis.

Don't sit down before the Queen does

Don't sit down until the Queen offers a chair. Credit: PA

The 45th US President should not sit down before the Queen does, and he should not remain sitting if the Queen stands.

Mr Trump should only take a seat if the Queen offers one, and as she stands again, he should too.

Don't turn your back on the Queen

When walking with the Queen, she should always be slightly ahead, solving the problem of showing the Queen your back.

However, once Mr Trump has had an audience with the Queen and is leaving a room, he should not turn immediately turn his back on the monarch and leave, instead, he should take a few steps backwards, and then it is acceptable to turn around and walk forwards to exit the room.

At one point in history it was unacceptable to show a Royal your back and people would would backwards when in the presence of one.

This rule has been relaxed in recent years, but it would still be possible for Mr Trump to walk in a sort-of-sideways manner so as not to show the Queen his back, but also see where he's going.

Don't eat before the Queen does and don't finish after her

If the Queen isn't eating, neither are you. Credit: PA

During the visit to Windsor Castle, both Trumps will enjoy the great British tradition of afternoon tea with her Majesty, which it turns out is an etiquette minefield in itself.

However, the one major the pair should follow (other than not sitting down before the Queen does) is to not start eating before the Queen does.

Similarly, once the Queen has finished eating, the Trumps should finish eating too. It doesn't matter if they've only had one bite out of a dainty cucumber sandwich, once the Queen is done, you are too, and the course will be cleared.

Other slightly more forgivable etiquette rules the Trumps should try to follow when enjoying afternoon tea with the Queen are not putting the milk into the cup before the tea, and putting cream on the scone before the jam (sorry Cornwall you're etiquette-ly wrong on this one).

Moreover, as Mr Harrold explains, the correct pronunciation of the controversial cake rhymes with "gone".

Yet so long as the Trumps don't tuck in before the Queen, the other rules probably aren't too hard and fast.

Don't worry about being sent to the Tower of London

The Tower of London is no longer a prison, luckily. Credit: PA

The Queen is known to be a lot more relaxed regarding Royal protocol than many of her successors, so any rule breaking will not see Mr Trump immediately carted off to the Tower Of London as they might have done in years gone by.